The present invention relates to methods, apparatus, and compositions for treating conditions of the cornea.
The cornea in the eye of a human or other mammalian subject can be modified by crosslinking the collagen within the cornea. A photoactivated crosslinking facilitator such as riboflavin is applied to the cornea. Light at a wavelength selected to activate the crosslinking facilitator is applied. Where the crosslinking facilitator is riboflavin, the light typically is ultraviolet (“UV”) or blue light. The activated facilitator causes crosslinking of the collagen within the cornea. The crosslinking changes the mechanical properties of the cornea. These changes can result in stabilization of pathological conditions, such as keratoconus, or in alterations to the shape of the cornea. This technique can be used to correct defects in vision such as myopia, hyperopia, or astigmatism. In some applications, the light is applied as a beam directed into the eye from a device remote from the eye.
In other applications, the light is directed into the cornea from a device that sits on the eye. For example, as disclosed in U.S. patent application Ser. No. 14/314,518 (“the '518 Application”) and U.S. Provisional Patent Application No. 61/839,016 (“the '016 Provisional”), the disclosures of which are hereby incorporated by reference herein and copies of which are annexed hereto as a part of this disclosure, light can be applied to the eye through a structure having a form, size, and shape resembling that of a contact lens such as a scleral contact lens. The structure may incorporate an optically dispersive element. Light may be directed into the dispersive element and dispersed so that the dispersed light passes into the eye from the dispersive element. This arrangement has numerous advantages. For example, the patient may be able to close his or her eye during the treatment, so that the structure is disposed between the eyelid and the eye. This helps to maintain adequate moisture on the surface of the cornea.
As also disclosed in the foregoing '518 Application and '016 Provisional, such a structure may be provided with one or more ports communicating with the surface of the device that overlies the cornea. Optionally, a liquid can be supplied through the ports so that the space between the device and the cornea remains filled with the liquid.
The degree of crosslinking depends in part upon the amount of crosslinking facilitator present in the collagen during light application and in part upon the amount of illumination applied to the eye. However, these factors alone apparently do not control the degree of crosslinking achieved.
Although the present invention is not limited by any theory of operation, current theory holds the oxygen present in the collagen layers of the cornea plays a role in the crosslinking reaction and that the crosslinking reaction can be limited by the amount of oxygen present. In the present disclosure, the concentration of oxygen in the cornea is referred to as the oxygen saturation of the cornea. Muller et al., Maximizing Efficacy of Accelerated Transepithelial Cross-linking, reports that when riboflavin is present in the cornea, the oxygen saturation of the cornea decreases rapidly upon irradiation of the cornea with UV light, and reports that crosslinking can be enhanced by exposing the cornea to gaseous oxygen rather than air during irradiation. However, further improvement would be desirable.